1. Field of the Invention
The invention relates to a drive apparatus having at least two electric motors as well as a central control common to all motors. The motors can be turned on and off from the central control.
2. Description of the Prior Art
In a known drive apparatus of this type, a multiple lead energy supply line leads to each of the motors from the central control in which the switches for all motors are collected. The expense for the wiring is, therefore, relatively large. This is especially true when the cable channels are narrow and poorly accessible, such as is the case in a motorized vehicle which requires a large number of electric motors, for example, for an adjustment of the seats.
The basic purpose of the invention is to create a drive apparatus of the above-mentioned type, which results in a low expense for the wiring even with a relatively large number of motors. This objective is achieved by the drive apparatus of the present invention.
Because all motors lie in series in a closed-circuit energy supply, only this single closed-circuit is necessary for the energy supply of all motors. This closed-circuit need have only one or two leads depending upon the type of motor used. It is true that an additional control line is necessary for the energy supply of the control device of each motor and the transmission of the control impulses. This control line can have the same course as the closed-circuit energy supply, so that this control line does not noticeably increase the expense for the wiring.
Depending upon whether it is necessary to keep two or more motors in operation at the same time, or whether it is sufficient to turn on various motors in succession, as necessary, and keep only a single motor in operation at one time, the energy supply will be different. In the latter case, it is sufficient to connect the selected motor with the current source in that its short-circuit device is opened. Such an instance will be present, for example, as a rule in a motor vehicle, when the motors of the drive apparatus serve to adjust the seats or other portions of the motor vehicle, such as the side windows and a sunroof, because all of these functions can be performed in succession, even if they are in one functional connection, such as can be the case in a seat adjustment. If several motors must run simultaneously, either a current limit can be provided for simultaneous operation with less than the maximum number of motors or, in a drive of more than one motor, a corresponding voltage increase can be provided. Here it is a prerequisite, however, that all motors can be fed simultaneously with the same direction of current. An impulse drive, in which the individual motors in the multiplex process are supplied with impulses in the case of simultaneous operation of several motors, would be free of this disadvantage. However, then at each impulse, the short-circuit device of the motor which received the last impulse and the short-circuit device of the motor which is to receive the next impulse would also have to be switched.